A technique of discriminating and identifying body tissue using a difference in the elastic modulus caused by elastic fiber, collagen fiber, fat, a thrombus, etc., making up tissue in a biological body is known as one of means for discriminating and identifying the properties of tissue in a biological body; a technique of measuring strain occurring when stress is applied to tissue in a biological body and finding a compressive elastic modulus from the relationship between the stress and the strain as shown in patent document 1 and a technique of finding the propagation characteristic of an elastic wave propagating in body tissue and finding mechanical impedance or elastic modulus from the propagation characteristic as shown in patent document 2, non-patent document 1, non-patent document 2, and non-patent document 3 are known.
If noise is contained in the motion velocity or move displacement of any of plural interest points or interest regions, the effect of the noise also appears in the calculated elastic modulus. Thus, a technique of removing noise if the target signal contains noise and interpolating with values at the times before and after the noise occurrence time or providing an ideal signal to approximate the signal, for example, as shown in patent document 3, patent document 4, and patent document 5 is known.
Patent document 1: JP-A-10-5226
Patent document 2: JP-A-62-172946
Patent document 3: JP-A-11-151242
Patent document 4: JP-A-2000-201932
Patent document 5: JP-A-2003-275211
Non-patent document 1: H. L. Oestreicher, “Field and Impedance of an Oscillating Sphere in a Viscoelastic Medium with an Application to Biophysics,” The Journal of the Acoustical Society of America, Vol. 23, No. 6, 1951.
Non-patent document 2: Y. Yamakoshi, J. Sato, T Sato, “Ultrasonic Imaging of Internal Vibration of Soft Tissue under Forced Vibration,” IEEE Trans. UFFC, Vol. 37, No. 2, 1990.
Non-patent document 3: K. Sunagawa, H. Kanai, Y. Koiwa, M. Tanaka, “Time-Frequency Analysis of Vibration Propagation from Intima to Adventitia of Arterial Wall,” 2002 IEEE Ultrasonics Symposium Proceedings, Vol. 2, 2002.